Method and apparatus for controlling mirror motion in light scanning arrangements

ABSTRACT

A method and apparatus of driving a motor in a light scanning arrangement. The method includes the following steps: (1) driving a drive coil with a drive signal to oscillate a scan mirror and a light beam reflected from the scan mirror; (2) generating a feedback signal having zero crossings during oscillation of the scan mirror by a feedback coil in proximity to the drive coil; (3) integrating the feedback signal to generate an integrated feedback signal; and (4) processing the integrated feedback signal to generate a periodic drive signal that has the same time period as the feedback signal.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to controlling the motion of ascan mirror employed for sweeping a light beam in electro-opticalreaders for reading indicia such as bar code symbols, or in imageprojectors for displaying images.

BACKGROUND

Electro-optical readers are well known in the art for electro-opticallytransforming a spatial pattern of graphic indicia, known as a symbol,into a time-varying electrical signal which is then decoded into data.Typically, a light beam generated from a light source is focused by alens along an optical path toward a target that includes the symbol. Thelight beam is repetitively swept along a scan line or a series of scanlines arranged in a raster pattern over the symbol by moving a scanminor located in the optical path. A photodetector detects lightscattered or reflected from the symbol and generates an analogelectrical signal. Electronic circuitry converts the analog signal intoa digitized signal having pulse widths corresponding to physical widthsof bars and spaces comprising the symbol, and a decoder decodes thedigitized signal into data descriptive of the symbol.

The repetitive sweeping of the light beam is performed by a drive,typically a motor having a rotor oscillatable about an axis. A permanentmagnet and the scan mirror are jointly oscillatable with the rotor. Themotor is driven by a drive coil wound on a bobbin that is locatedphysically close to the permanent magnet. A feedback coil is also woundon the same bobbin. In response to an alternating voltage drive signalapplied to the drive coil, the electromagnetic field produced by thedrive coil interacts with the permanent magnetic field of the magnet,thereby jointly moving the magnet and the mirror. The motor and mirrorassembly form a resonant mechanical structure, where the naturalfrequency of this structure determines oscillation frequency. Thefrequency of the drive signal in the drive coil is the same as the rotormotion, with one cycle of the drive signal corresponding to one cycle ofrotor motion. The amplitude of the drive signal in the drive coil isproportional to the velocity of the rotor motion. The polarity of thedrive signal in the drive coil is dependent on the direction of rotormotion such that a positive half cycle of the drive signal indicatesthat the rotor is moving in one drive direction, and a negative halfcycle indicates that the rotor is moving in the opposite drivedirection. Zero crossings of the drive signal occur when the rotorreaches its maximum travel at each end of a respective scan line. Ateach zero crossing, the rotor stops for an instant and reverses drivedirection.

The feedback coil is useful for a variety of purposes. It generates analternating voltage signal, known as a feedback signal, due to themovement of the magnet. The frequency and polarity of the feedbacksignal generated in the feedback coil corresponds to the frequency andpolarity of the moving magnet. An electrical drive monitoring circuit isoften employed to monitor the amplitude of the feedback signal and, forexample, turn the light source off if the amplitude falls below apredetermined threshold, thereby indicating that the drive ismalfunctioning. An electrical closed loop control circuit is also oftenemployed to process the feedback signal to make decisions about how tocontinue driving the motor. Still another electronic circuit that isoften employed processes the zero crossings of the feedback signal toderive a start-of-scan (SOS) signal that represents rotor motion and isused to synchronize the scan lines.

In some implementations, the electrical closed loop control circuit isused to regulate the peak values of the feedback signal generated fromthe feedback coil. If the magnitude of a peak value (either positivepeak or negative peak) is smaller than a desired (or target) value, theelectrical closed loop control circuit will try to increase the currentapplied to the drive coil in order to increase the magnitude of the peakvalue. On the other hand, if the magnitude of a peak value (eitherpositive peak or negative peak) is larger than a desired (or target)value, the electrical closed loop control circuit will try to decreasethe current applied to the drive coil in order to decrease the magnitudeof the peak value.

With the electrical closed loop control circuit described above, eachpeak value of the feedback signal can be maintained close to certaindesired (or target) value. This electrical closed loop control circuitenables the peak velocity of the scan mirror to be regulated, becausethe feedback signal generated from the feedback coil is proportional tothe first derivative of scan mirror's displacement function. Thiselectrical closed loop control circuit can also be used to regulate thescan amplitude of the scan mirror, provided that the motor's operatingfrequency remains unchanged. In some operation environments, however,the motor's operating frequency can be changed for variety of reasons.Therefore, with the electrical closed loop control circuit describedabove, even if each peak value of the feedback signal can be maintainedclose to certain desired (or target) value, the scan amplitude of thescan mirror will change in proportion to any change in motor frequency.Such change will introduce amplitude errors. The scan amplitude of thescan mirror can be different than, or can drift away from, the desired(or targeted) scan amplitude.

Accordingly, in some operation environments, it is desirable to havecertain electrical closed loop control circuit that can maintain thescan amplitude of the scan mirror close to a constant value, as animprovement of the circuit that merely regulates the peak velocity ofthe scan mirror.

SUMMARY

In one aspect, the invention is directed to a method of driving a motorin a light scanning arrangement. The method includes the followingsteps: (1) driving a drive coil with a drive signal to oscillate a scanmirror and a light beam reflected from the scan mirror; (2) generating afeedback signal having zero crossings during oscillation of the scanmirror by a feedback coil in proximity to the drive coil; (3)integrating the feedback signal to generate an integrated feedbacksignal; and (4) processing the integrated feedback signal to generatethe drive signal as a square wave having vertical edges respectivelycorresponding to the zero.

In another aspect, the invention is directed to a motor drive circuit ina light scanning arrangement. The motor drive circuit includes a drivecoil and a feedback coil. The drive coil driven by a drive signal tooscillate a scan mirror and a light beam reflected from the scan mirror.The feedback coil generates a feedback signal having zero crossingsduring oscillation of the scan mirror. The motor drive circuit alsoincludes circuitry for integrating the feedback signal to generate anintegrated feedback signal. The motor drive circuit further includescircuitry for processing the integrated feedback signal to generate thedrive signal as a square wave having vertical edges respectivelycorresponding to the zero crossings.

Implementations of the invention can include one or more of thefollowing advantages. The scan magnitude of the scan mirror can bedirectly regulated and be maintained close to certain constant. Theseand other advantages of the present invention will become apparent tothose skilled in the art upon a reading of the following specificationof the invention and a study of the several figures of the drawings.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a diagrammatic view of a hand-held instrument forelectro-optically reading indicia;

FIG. 2 is a block diagram of some of the components in the instrument ofFIG. 1;

FIG. 3 is a block diagram further detailing the arrangement of FIG. 2;

FIG. 4 is a series of signals generated in the circuit of FIG. 3;

FIG. 5 is a block diagram of the arrangement of FIG. 2 with additionalcomponents for use in the instrument of FIG. 1; and

FIG. 6 is a series of signals generated in the circuit of FIG. 5.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION

Reference numeral 220 in FIG. 1 identifies an electro-optical reader forelectro-optically reading indicia, such as bar code symbol 224, locatedin a range of working distances therefrom. The reader 220 has a pistolgrip handle 221 and a manually actuatable trigger 222 which, whendepressed, enables a light beam 223 to be directed at the symbol 224.The reader 220 includes a housing 225 in which a light source 226, alight detector 227, signal processing circuitry 228, and a battery pack229 are accommodated. A light-transmissive window 230 at a front of thehousing enables the light beam 223 to exit the housing, and allows light231 scattered off the symbol to enter the housing. A keyboard 232 and adisplay 233 may advantageously be provided on a top wall of the housingfor ready access thereto.

In use, an operator holding the handle 221 aims the housing at thesymbol and depresses the trigger. The light source 226 emits a lightbeam which is optically modified and focused by an optical focusingassembly 235 to form a beam spot on the symbol 224. The beam passesthrough a beam splitter 234 to a scan mirror 236 which is repetitivelyoscillated at a scan rate of at least 20 scans a second by a motor drive238. The scan mirror 236 reflects the beam incident thereon to thesymbol 224 and sweeps the beam spot in scans across the symbol in a scanpattern. The scan pattern can be a scan line extending lengthwise alongthe symbol along a scan direction, or a series of scan lines arrangedalong mutually orthogonal directions, or an omnidirectional pattern,just to name a few possibilities.

The reflected light 231 has a variable intensity over the scan patternand passes through the window 230 onto the scan mirror 236 where it isreflected onto the splitter 234 and, in turn, reflected to thephotodetector 227 for conversion to an analog electrical signal. Thesignal processing circuitry 228 digitizes and decodes the signal toextract the data encoded in the symbol.

The drive motor 238 is shown in more detail in FIG. 2 with a drive coil240 and a feedback coil 242 both wound on a common bobbin. The signalprocessing circuitry 228 includes a control microprocessor 246 operativefor sending a control signal to a drive circuit 244 which, in turn,sends a drive signal to the drive coil 240 to generate anelectromagnetic field that interacts with a permanent magnet 248 anddrives the motor 238.

The drive circuit 244 is shown in its entirety in FIG. 5, withexplanatory signal waveforms depicted in FIG. 6. A motor drive front endcircuit 100 depicted in FIG. 5 is shown in more detail in FIG. 3, withexplanatory signal waveforms depicted in FIG. 4. The drive circuit 244is advantageously implemented in an application specific integratedcircuit (ASIC) 250 which, together with the microprocessor 246,constitute the signal processing circuitry 228.

As previously mentioned, a square wave drive signal is conducted to thedrive coil 240 to cause the scan mirror 236 to oscillate. At the sametime, the jointly mounted magnet 248 oscillates and generates a feedbacksignal in the feedback coil 242. Crosstalk between the coils 240, 242only occurs at the amplitude changes of the square wave drive signal,that is, at its vertical edge transitions. The resulting corruptedfeedback signal is shown in FIG. 4 and is conducted to the track andhold circuit 102 having a capacitor 104. An edge-triggered one shotcircuit 106 is operatively connected to a switch 108 in the track andhold circuit. The output of the track and hold circuit is conducted toan adjustable gain amplifier 110 whose output is conducted through a DCvoltage offset adjustment circuit 112. The output of the adjustmentcircuit 112 is connected to a zero crossing detector 114 operative fordetecting zero crossings in the feedback signal and for generating theaforementioned SOS signal. The output of the zero crossing detector isconnected to the one shot circuit 106.

The output of the adjustment circuit 112 is also connected to anintegration circuit 180 though a buffer amplifier, such as an inverter115. The integration circuit 180 includes an operational amplifier 182,a capacitor 184, and a switch 186. The switch 186 can be opened orclosed under the control of the edge-triggered one shot circuit 106.

In operation, the track and hold circuit 102 monitors the corruptedfeedback signal whose voltage is used to charge the capacitor 104. Ateach zero crossing of the feedback signal, the one shot circuit 106 istriggered to generate the command signal. The command signal opens theswitch 108 at each zero crossing, effectively removing the crosstalkpresent at each zero crossing. The uncorrupted feedback signal shown inFIG. 4 has the same general shape as the corrupted feedback signal,except the crosstalk at each zero crossing has been removed.

In operation, the command signal also closes the switch 186 at each zerocrossing to reset the voltage across the integration capacitor 184. Whenthe switch 186 is reopened shortly after the closing of the switch ateach zero crossing, the integration circuit 180 will start to integratethe uncorrupted feedback signal received from the adjustment circuit112. The integration circuit 180 will generate an integrated feedbacksignal at the output of the integration circuit. The integrated feedbacksignal is also shown in FIG. 4.

In an ideal situation, if the feedback signal generated from thefeedback coil 242 is not corrupted, this feedback signal can be directlyintegrated by the integration circuit 180 after the feedback signal isadjusted for certain offset. In addition, if the switch 186 is reopenedalmost instantaneously after the closing of the switch at each zerocrossing to initiate the integration of the feedback signal generatedfrom the feedback coil 242, the integrated feedback signal at the outputof the integration circuit 180 will be proportional to the angulardisplacement of the scan mirror, where the angular displacement ismeasured from the maximum angular displacement when the scan mirrorreverses its scanning direction. If the peak of the integrated feedbacksignal is compared with certain reference levels, as shown in FIG. 5,the scan magnitude of the scan mirror can be directly regulated with thedrive circuit 244. Consequently, the scan amplitude of the scan mirrorcan be maintained close to certain constant.

In some real situation, even if the feedback signal generated from thefeedback coil 242 is corrupted, this feedback signal can still bedirectly integrated by the integration circuit 180 after the feedbacksignal is adjusted for certain offset. If the switch 186 is reopenedafter a small time delay as measured from the closing of the switch ateach zero crossing, the integrated feedback signal at the output of theintegration circuit will be offset by a small offset error from an idealvalue, where the ideal value will be proportional to the angulardisplacement of the scan mirror as measured from the maximum angulardisplacement when the scan mirror reverse its scanning direction. Thissmall offset error generally is proportional to the small time delay asmeasured from the closing of the switch at each zero crossing. Thissmall offset error can be neglected, if the magnitude of the feedbacksignal generated from the feedback coil 242 during the time period ofthe small time delay is much smaller than the peak magnitude of thefeedback signal. In a situation that the small offset error can beneglected, the scan magnitude of the scan mirror can still be directlyregulated and be maintained close to certain constant with the drivecircuit 244 as shown in FIG. 5, even if the feedback signal generatedfrom the feedback coil 242 does not pass through the track and holdcircuit 102.

As also depicted in FIG. 4, during the initial start-up of the drivemotor, that is prior to reaching the steady-state condition, the voltageof the peaks of the uncorrupted feedback signal successively increases,while the corresponding magnitude of the square waves of the drivesignal successively decrease. The magnitude of the square waves onlychanges at SOS boundaries, that is, at the zero crossings.

Turning again to FIG. 5, the integrated feedback signal from the frontend circuit 100 is connected to a positive peak detector (PPD) 116 and anegative peak detector (NPD) 118. The peak outputs of the PPD and NPDare conducted to negative inputs of error amplifiers 120, 122. Positiveand negative reference voltages are conducted to the positive inputs ofthe error amplifiers. The outputs of the error amplifiers are connectedto a commutator switch 124 under the control of the SOS signal. Theoutput of the switch 124 is conducted back to the drive coil 240 via akick signal switch 126, and a push-pull drive having an inverter 128 andan amplifier 130 in one branch is connected to one end of the drive coil240, and an amplifier 132 in another branch is connected to the oppositeend of the drive coil 240. As shown, the circuit of FIG. 5 includes apositive feedback arrangement (via the SOS signal path) that passesthrough a motor assembly (FIG. 2) where the natural frequency of themotor determines the oscillation frequency of the loop, and a negativefeedback arrangement (via the integrated feedback signal path) thatcontrols the amplitude of the motor.

Timing circuits 134 are used to generate a kick signal for the kickswitch 126, a reset NPD signal to reset the NPD 118, a reset PPD signalto reset the PPD 116, and the SOS signal to control the commutatorswitch 124. All of these signals are depicted in FIG. 6.

In operation, the integrated feedback signal from the front end circuit100 is processed to produce a square wave drive signal. Moreparticularly, the integrated feedback signal is peak detected by the PPDand the NPD and compared to a fixed reference value. The result of thiscomparison is a PPD signal and an NPD signal which closely resemble asquare wave at the outputs of the error amplifiers. The switch 124 isswitched in synchronism with the SOS signal, to produce a more idealsquare wave drive signal that is in proportion to the amplitude errorthat was detected by the respective error amplifier during the previousSOS state. In other words, a correction during a current SOS state ismade based on the voltage peak detected during the previous SOS state.Each of the PPD and the NPD is reset on alternate SOS edges so that newinformation can be evaluated.

Referring again to FIG. 6, the first pulse labeled “kick” of the drivesignal that is delivered to the drive coil via kick switch 126 isgenerated by timing circuits 134 and does not depend on feedbackinformation. The second pulse labeled f_((B1)) is derived fromevaluating peak velocity information B1 that was acquired during theprevious SOS period while the motor was being kicked. The magnitude off_((B1)) is determined by the corresponding error amplifier 120 or 122.The third pulse labeled f_((A1)) is derived from evaluating peakvelocity information A1 that was acquired during the previous SOSperiod. Successive pulses are processed in the same way. The drivesignal preferably has a 50% duty cycle synchronized to the SOS signal.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter ties in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

1. A motor drive circuit in a light scanning arrangement, comprising: a)a drive coil driven by a drive signal to oscillate a scan mirror and alight beam reflected from the scan mirror; b) a feedback coil forgenerating a feedback signal having zero crossings during oscillation ofthe scan mirror, the feedback coil being in proximity to the drive coiland being corrupted by cross-coupling between the coils at each zerocrossing; c) circuitry for minimizing the cross-coupling at each zerocrossing to generate an uncorrupted feedback signal; d) circuitry forintegrating the uncorrupted feedback signal to generate an integratedfeedback signal; and e) circuitry for processing the integrated feedbacksignal and the uncorrupted feedback signal to generate the drive signalas a square wave having vertical edges respectively corresponding to thezero crossings.
 2. The motor drive circuit of claim 1, wherein the scanmirror has a permanent magnet mounted thereon for joint oscillationtherewith, and wherein the square wave drive signal generates anelectromagnetic field which interacts with a permanent magnetic field ofthe magnet to oscillate the mirror and the magnet in opposite drivedirections at a drive frequency.
 3. The motor drive circuit of claim 1,further comprising circuitry for generating a start-of-scan signal fromthe uncorrupted feedback signal.
 4. The motor drive circuit of claim 3,wherein the circuitry for processing comprises circuitry for processingthe integrated feedback signal and the start-of-scan signal to generatethe drive signal as a square wave having vertical edges respectivelycorresponding to the zero crossings.
 5. The motor drive circuit of claim1, wherein the circuitry for integrating the uncorrupted feedback signalcomprises circuitry for charging an integration capacitor in anintegration circuit.
 6. The motor drive circuit of claim 5, wherein thecircuitry for integrating the uncorrupted feedback signal furthercomprises circuitry for driving a switch into a closing state at eachzero crossing to discharge the integration capacitor.
 7. The motor drivecircuit of claim 1, wherein the processing circuitry includes a positivepeak detector and a negative peak detector having inputs to which theintegrated feedback signal is conducted, and having outputs from whichpositive and negative peak voltages are conducted to first terminals oferror amplifiers, the error amplifiers having second terminals connectedto positive and negative reference voltages.
 8. The motor drive circuitof claim 7, wherein the error amplifiers have outputs connected to acommutator switch which is switched between the outputs of the erroramplifiers to generate the square wave drive signal.
 9. A method ofdriving a motor in a light scanning arrangement, comprising the stepsof: a) driving a drive coil with a drive signal to oscillate a scanmirror and a light beam reflected from the scan mirror; b) generating afeedback signal having zero crossings during oscillation of the scanmirror by a feedback coil in proximity to the drive coil, the feedbackcoil being corrupted by cross-coupling between the coils at each zerocrossing; c) minimizing the cross-coupling at each zero crossing togenerate an uncorrupted feedback signal; d) integrating the uncorruptedfeedback signal to generate an integrated feedback signal; and e)processing the integrated feedback signal and the uncorrupted feedbacksignal to generate the drive signal as a square wave having verticaledges respectively corresponding to the zero crossings.
 10. The methodof claim 9, and the step of mounting a permanent magnet on the scanmirror for joint oscillation therewith, and wherein the square wavedrive signal generates an electromagnetic field which interacts with apermanent magnetic field of the magnet to oscillate the mirror and themagnet in opposite drive directions at a drive frequency.
 11. The methodof claim 9, and the step of generating a start-of-scan signal from theuncorrupted feedback signal.
 12. The method of claim 11, and wherein thestep of processing comprises processing the integrated feedback signaland the start-of-scan signal to generate the drive signal as a squarewave having vertical edges respectively corresponding to the zerocrossings.
 13. The method of claim 9, wherein the step of integratingthe uncorrupted feedback signal comprises a step of charging anintegration capacitor in an integration circuit.
 14. The method of claim13, wherein the step of integrating the uncorrupted feedback signalfurther comprises a step of driving a switch into a closing state ateach zero crossing to discharge the integration capacitor.
 15. Themethod of claim 9, wherein the processing step is performed by detectingpositive and negative voltage peaks in the integrated feedback signal,and by comparing the positive and negative voltage peaks with referencevoltages to obtain positive and negative signals.
 16. The method ofclaim 15, wherein the processing step is performed by switching acommutator switch between the positive and negative signals to obtainthe square wave drive signal.
 17. A motor drive circuit in a lightscanning arrangement, comprising: a) a drive coil driven by a drivesignal to oscillate a scan mirror and a light beam reflected from thescan mirror; b) a feedback coil for generating a feedback signal havingzero crossings during oscillation of the scan mirror, the feedback coilbeing in proximity to the drive coil; d) circuitry for integrating thefeedback signal to generate an integrated feedback signal; and e)circuitry for processing the integrated feedback signal to generate aperiodic drive signal that has the same time period as the feedbacksignal.
 18. The motor drive circuit of claim 17, wherein the periodicdrive signal is a square wave having vertical edges respectivelycorresponding to the zero crossings of the feedback signal.
 19. Themotor drive circuit of claim 17, wherein the time period of the feedbacksignal is determined by the motor's natural frequency.
 20. The motordrive circuit of claim 17, wherein the circuitry for integrating thefeedback signal comprises circuitry for charging an integrationcapacitor in an integration circuit.
 21. The motor drive circuit ofclaim 20, wherein the circuitry for integrating the feedback signalfurther comprises circuitry for driving a switch into a closing state ateach zero crossing to discharge the integration capacitor.
 22. The motordrive circuit of claim 17, wherein the processing circuitry includes apositive peak detector and a negative peak detector having inputs towhich the integrated feedback signal is conducted, and having outputsfrom which positive and negative peak voltages are conducted to firstterminals of error amplifiers, the error amplifiers having secondterminals connected to positive and negative reference voltages.
 23. Themotor drive circuit of claim 22, wherein the error amplifiers haveoutputs connected to a commutator switch which is switched between theoutputs of the error amplifiers to generate the square wave drivesignal.
 24. A method of driving a motor in a light scanning arrangement,comprising the steps of: a) driving a drive coil with a drive signal tooscillate a scan mirror and a light beam reflected from the scan mirror;b) generating a feedback signal having zero crossings during oscillationof the scan minor by a feedback coil in proximity to the drive coil; d)integrating the feedback signal to generate an integrated feedbacksignal; and e) processing the integrated feedback signal to generate aperiodic drive signal that has the same time period as the feedbacksignal.
 25. The method of claim 24, wherein the periodic drive signal isa square wave having vertical edges respectively corresponding to thezero crossings of the feedback signal.
 26. The method of claim 24,wherein the time period of the feedback signal is determined by themotor's natural frequency.
 27. The method of claim 24, wherein the stepof integrating the feedback signal comprises a step of charging anintegration capacitor in an integration circuit.
 28. The method of claim27, wherein the step of integrating the feedback signal furthercomprises a step of driving a switch into a closing state at each zerocrossing to discharge the integration capacitor.
 29. The method of claim24, wherein the processing step is performed by detecting positive andnegative voltage peaks in the integrated feedback signal, and bycomparing the positive and negative voltage peaks with referencevoltages to obtain positive and negative signals.
 30. The method ofclaim 29, wherein the processing step is performed by switching acommutator switch between the positive and negative signals to obtainthe square wave drive signal.
 31. A scanner for reading indiciacomprising: an oscillating mirror assembly having an magnet attachedthereon; a drive coil for driving the magnet that controls the minor; apickup coil for sensing the movement of the magnet; and wherein theoutput of the pickup coil is integrated to provide an mirror amplitudeinformation signal that is used in a feedback arrangement where the scanamplitude of the mirror is regulated.